Gas turbines are used in many fields to drive generators or machines. The energy content of a fuel is thereby used to generate a rotational movement of a turbine shaft. For this purpose the fuel is burned in a plurality of burners, with compressed air being supplied by an air compressor. Combustion of the fuel produces a high-temperature working medium at high pressure. This working medium is directed into a turbine unit connected downstream from the respective burner, where it expands in a manner that provides work output. A separate combustion chamber can be assigned here to each burner, whereby the working medium flowing out of the combustion chambers can be combined before or in the turbine unit. Alternatively the gas turbine can however also be designed as what is known as an annular combustion chamber, with which a majority, in particular all, of the burners open out into a common, generally annular, combustion chamber.
When designing such gas turbines, both the achievable output and a particularly high level of efficiency are generally the design objectives. An increase in efficiency can essentially be achieved for thermodynamic reasons by increasing the exit temperature at which the working medium flows out of the combustion chamber and into the turbine unit. Temperatures of around 1200° C. to 1500° C. are therefore aimed at and achieved for such gas turbines.
With such high working medium temperatures however the components and parts exposed to said medium are exposed to high thermal loads. In order to ensure a comparatively long life for the components in question, whilst nevertheless maintaining a high level of reliability, an embodiment comprising particularly heat-resistant materials is required as is cooling of the relevant components, such as the combustion chamber and the turbine unit. The combustion chamber and the moving parts of the turbine unit in particular are however subject to increased wear and tear due to the thermal load and general attrition due to the throughflow of the working medium, with the result that gas turbines have to be regularly maintained so that damaged components can be replaced or repaired.
The turbine unit adjacent to the combustion chamber in the direction of flow of the working medium generally comprises a turbine shaft which is connected to a plurality of rotatable blades which form series of blades in an overlapping ring shape. The turbine unit also comprises a plurality of fixed vanes, which are also attached in an overlapping ring shape to the inner housing of the turbine thereby forming series of vanes. The blades are used to drive the turbine shaft by transmitting the pulse from the working medium flowing through the turbine unit, while the vanes are used to direct the flow of the working medium between two consecutive series of blades or blade rings viewed in the direction of flow of the working medium in each instance.
As the rotational movement of the turbine shaft is generally used to drive the air compressor connected upstream from the combustion chamber, this is extended beyond the turbine unit, so that the turbine shaft is surrounded in a toroidal manner by the annular combustion chamber in the area of the annular combustion chamber connected upstream from the turbine.
The combustion area is thereby bounded by an annular outer wall on the one hand and an annular inner wall located therein on the other hand. The inner wall of the combustion chamber generally comprises two or more individual parts for this purpose, which are screwed together on their side facing the turbine shaft.
This annular combustion chamber structure however has some disadvantages, as the inner wall of the combustion chamber is not accessible for maintenance work. This means that for maintenance work on the inner wall, the upper parts of the compressor and turbine blade supports have to be dismantled so that the turbine shaft can be disassembled with the inner wall of the combustion chamber, thereby allowing access to said inner wall. Assembly work is therefore very labor- and time-intensive. The comparatively long downtime of the gas turbine means that downtime costs are incurred in addition to gas turbine assembly costs, resulting in comparatively very high overall costs for maintenance and repair work on the gas turbine.